The invention relates to an article formed from fused quartz. More particularly, the invention relates to an article comprising fused quartz and having an outer coating containing metal cations. Even more particularly, the invention relates to a fused quartz article having an outer coating containing metal cations, wherein the fused quartz undergoes a transition to a cristobalite crystal structure at a temperature of at least about 1000° C. The invention also relates to a method of coating a fused quartz article with a coating containing a plurality of metal cations.
Quartz (also referred to hereinafter as “fused quartz”) is used to form articles, such as tubes and crucibles, which are used in the processing of products, such as optical fibers and semiconducting materials, at high temperatures. Quartz articles undergo viscous creep at high temperatures and are thus prone to failure. Quartz muffle tubes, for example, are used throughout the fiber optics industry during the sintering step in optical-quality glass boule production. In the sintering application, tubes are usually suspended vertically, and sintering takes place at temperatures around 1500° C. At such temperatures, the fused quartz muffle tubes undergo viscous creep, which can lead to muffle tube failure.
Fused quartz articles, such as muffle tubes and crucibles, have limited service lifetimes due to viscous creep occurring at high temperatures of operation. Therefore, what is needed is a fused quartz article that is resistant to creep at high temperatures. What is also needed is a method of treating a fused quartz article to improve the creep resistance of the article.